Does Vegetable Oil Go Bad? (Why It’s So Important)

People are replacing regular cooking oil with vegetable oil due to its properties.

The shift is likely to increase as more people are unraveling the tremendous health benefits of these oils.

Moreover, people are also becoming inclined to the vegan lifestyle which is another reason for the popularity of vegetable oil.

The misconception is that vegetable and other cooking oil has a long shelf life and that they do not go bad, however, it is not the case.

So, if you have been using the year-old vegetable oil in your kitchen, then it is time to change it because it might go bad soon enough.

In recent years, the trend of using vegetable oil has soared significantly.


What Are Vegetable Oils

Plant-based oils are derived from nuts and fruits.

These odorless oils are polyunsaturated fatty acids. These are liquid at room temperature, unlike animal fats such as butter and lard which remain solid.


Vegetable Oil Formation

Vegetable oils are usually acquired by heating, burning, or cracking the source.

Afterward, it is refined to make it suitable for human consumption. The process also removes any odors and sometimes puts additional chemicals into the composition of the oils.

Some vegetable oils are used for exquisite taste. These may include sesame, olive, corn, and sunflower oil.

These steps, however, leave some of the oil content in the source.

All oil companies have the goal to completely extract the raw material and ensure that the oil within the seeds or the fruits does not go to waste.

They perform an additional step that can completely drain the oil from the source material.

The procedure is termed chemical extraction and usually involves the heating of plant-based compounds.

Hexane is the typical solvent used for the process however, it has been attributed to increasing pollution and carbon input. Therefore, companies are striving for more eco-friendly solvents.

Enzyme-assisted extraction and terpenes are more effective substances for acquiring oils from the seeds.

In the next step, the oils are refined to remove all kinds of toxins.

The process makes vegetable oils fit for humans. Vegetable oils have numerous health benefits because they are unsaturated fats.

They are an efficient source of good cholesterol and are useful for your heart health. The effects of vegetable oils may also depend on the particular type you select for your needs.

Olive oil is an excellent source of antioxidants.

Olive oil lowers your chances of stroke and diabetes. Sunflower oils in contrast are highly prevalent in industries because they do not burn despite continuous high heat.

The chemical aspects of vegetable oil formation imply that vegetable oils have a limited span.

It is advisable to use the oils within this timeline to avoid potential health risks.

Organic substances that are produced without the involvement of any chemicals can be used over and over again. However, that is not the case with vegetable oils.

Despite the multiple health benefits provided by these oils, it is only unwise to think that these oils can last long.


How Does Vegetable Oil Get Spoiled

There are numerous ways through which vegetable oils go bad and can no longer be used.

The following are some of them:



Vegetable oils have oxidative stability which helps them maintain their chemical composition. As a result, they remain in pristine condition every time you cook with them.

The oxidative stability is targeted due to exposure to various environmental stimuli.

These include heat and water which can oxidize the oil. Moreover, certain types of fats and oils are more prone to oxidation. These include polyunsaturated fats.

Most vegetable oils are either monounsaturated or polyunsaturated which means that they double bonds.

The double bonds between the oil components can be one or two.

Such oils can break down and degrade instantly due to environmental factors. Oxygen usually reacts with the oil components.

The process results in the formation of peroxides which further increase the pace of oxidation. An oxidized oil can cause several harmful impacts on your body.

The reactive oxygen molecules can cause oxidative stress in your body which in turn damages your liver, causes cancers, and impact your heart.



Oil and water do not mix.

It is a natural phenomenon that occurs due to the varying chemical composition of both compounds. Whenever you use oil with water it evaporates.

Pouring it into a pan will also produce steam as water becomes heated you will notice bubbles of water on the oil surface.

Mixing water in the oil may reduce its quality and accelerate the degradation process. Intense foaming may occur in the oil which may produce separate oil and water layers.

The oxygen in the water molecule formulates a bond with the carbon in the oils. The double or single bond between the carbon atoms starts deteriorating as the vegetable oil becomes stale.

The hydration of the oils becomes more favorable under such conditions.

The process becomes accelerated in the presence of heat, UV, or sunlight. You must avoid adding the two substances together.

Moreover, if you add water to the oils while cooking it will expel in all directions.

It mostly occurs when you instantly put frozen food items into piping hot oil.

The oil explosion can be dangerous because it contacts your skin and can cause burns. In some cases, a fire hazard may also erupt which can be quite difficult to manage.


Overusing the Oil

Reusing vegetable oil is quite common in households and restaurants.

As oil prices keep on soaring, people are becoming more prudent with their oil consumption. Therefore, they store the vegetable oil after every cooking session and use it again.

The practice is more prevalent in Asian countries.

Studies suggest that long-term usage of vegetable oils can potentially harm your organs.

The oil starts degrading every time you reuse it. It can be readily oxidized by air particles. Such oils can more swiftly emit smoke. The smoke point is an indicator that the oil is being heated at a very high rate.

The residue of the frozen or fried food also sinks to the bottom of the reused vegetable oils.

High temperatures and constant use of the same oil can cause the formation of trans fatty acids. These harmful fats are produced even in the most high-quality vegetable oils if you conduct such practices.


Signs That Your Oil Has Gone Bad

Following are the telltale signs of vegetable oil that have gone bad:


Expiry Date

Every vegetable oil can come with an expiry date.

Most manufacturers produce vegetable oils that can last up to 12 months. On average vegetable oils can even remain preserved for 24 months.

If you have opened the can then it may last for up to 6 months.

Unused bottles have a high chance of going bad within the next few months. The higher the quality of your vegetable oil, the more prolonged its shelf life will be.

You must use premium vegetable oils if you intend to store them for a long time.

The best-before dates are usually mentioned on the cans.

Most oil packets come with an estimate for the total shelf life of the vegetable oil. Therefore, you will mostly find phrases like use within 18 months or 12 months.

It is recommended to stop using the oil once the expiry date reaches.

In some cases, people keep on using the oil because its quality remains untarnished. Moreover, such vegetable oils do not pose any threat to your health. Therefore, it is mandatory to search for other signs.



Spoiled vegetable oil will usually have a rancid smell.

The pungent odor will spread into your kitchen. You can easily detect the smell when you use the oil. In some cases, it will be present in your whole household if you keep on using it.

Oxidation usually leads to bad odors in the oils.

The accumulation of free radicals makes your oil rancid. If you keep on cooking with such vegetable oils the food will taste disgusting.

The rancid oils result due to the formation of a bond between carbon molecules in the oil and oxygen in the air.

As the oils start degrading the carbon bonds become weaker and are more susceptible to the oxygen in the air. Moreover, if you store the vegetable oils in sunlight or a place where UV radiation can reach then they will also become spoiled and rancid.

The light promotes the activity of the reactive oxygen molecules in the air or water.

These develop an affinity for the carbon in vegetable oils. Such oils will have a musty taste that will spoil your food.



The presence of mold around your vegetable oil container is evidence of spoiled oil.

Vegetable oils provide a highly nutritious space for mold to grow and thrive. The carbon in vegetable oils acts as an energy source for the fungal body.

Research suggests that fats and lipid-based substances prove to be an efficient anchor for fungal survival.

Colonies of fungus can be cultivated on various vegetable oils.

They utilize the raw molecules within the vegetable oil to give rise to fungal hyphae. As the network of hyphae develops the fungal body called mycelium becomes more firmly attached to the oil container.

Olive and linseed oils are the most preferable growth medium for various fungal species.

These oils also provide an adhesion surface to the growing fungal spores. If you place the oil in a damp place then the mold growth will enhance.


Reused Oils

Reused oils also have a high probability of being spoiled.

These oils already have a damaged carbon bond and exposure to air exacerbates the condition.

Over time such vegetable oils may also start giving off a rancid odor however, in the absence of the smell the appearance of the signals its deterioration.

Most reused oils also have a black greasy substance that accumulates at the end of the containers.

These oils burn instantly, and the utensils become covered with grease. However, the food particles become the debris in the oil. Food cooked in such vegetable oils will have a sour taste and a greasy texture.


Storing the Vegetable Oil

Following are some of the ways to effectively store vegetable oil and enhance urs shelf life.

  • Open the container as soon as you buy it
  • Do not open the entire oil bottle every time you cook
  • Add some of the oil to a small bottle and keep it nearby the stove
  • Keep the oil container in a dark place
  • Store it in a cool region and if you live in a hot climate try putting it in the refrigerator at particular intervals
  • Tightly close the seal of the bottle after use
  • In case of crystallization within the oil leave the bottle cap open for sometime
  • Keep away from direct sunlight and heat
  • Do not add water to the oil bottle
  • Try using the oil within the first year of the purchase
  • Do not reuse the same oil over and over again
  • In case of reusing ensure that you cook the same food every time in that oil
  • If the flour coating or any mixture is left in the oil do not use it for any other dishes
  • Use high-quality premium oils

Vegetable oils can go bad instantly if the storage conditions are not ideal.

Ensure that you do not stock vegetable oil containers in your house. Use them according to your requirement and in smaller portions. Keep the storage environment optimal to maximize their shelf life.



1. Which Vegetable Oils Should I Use?

The choice of vegetable oil will depend upon your nutrition requirements.

You can use coconut oil for getting healthier skin and teeth. For reducing the incidence of chronic disorders like diabetes or heart disease you can use olive oil.


2. Are Vegetable Oils a Healthy Alternative?

Yes, vegetable oils are more nutritious and beneficial.

They have antioxidant properties. The unsaturated fats provide you with a substantial amount of good cholesterol. They reduce your chances of getting heart disease. They also maintain your hepatic health.


3. Can I Use Vegetable Oil After It Expires?

Yes, you can use vegetable oil after the expiry in certain conditions.

If the quality of the oils remains unaltered you can use it. You can also use it if there is no rancid odor and the oil does not destroy the taste of your food.